High Pressure Pump

[HGilliland21]

The environmental lab I work for has a Metrohm 881 Compact IC Pro. Since I have ran the instrument the High-Pressure pump has been rebuilt twice in the past year. Both times, I suspected the problem to be behind the pump because all parts looked fine within it. Upon reassembling the pump, the pressure seemed to be in range and stable, so I continued with my runs.

However, last night in the middle of the run, the pressure dropped out again. This morning I checked the flow and immediately knew the pump had quit again. I took the pump apart, rinsed the inlet/outlet valves and replaced the pistons/seals, and pressure is back to normal. Although pressure is reading normal, it doesn't seem to be stable as it already has dropped from 7.9 to 7.5 MPa in a couple of hours and I have a strong feeling it will drop out again tonight. Also, my retention times have shifted heavily and according to Metrohms manual for the instrument, it could be "defective high pressure pump", among other things, but I have a feeling its the pump since I have had issues with it (eluent and air bubbles are not the issue). I am wondering if anyone has had any issues with the actuators that are behind the pump and not the pump itself. Upon checking the flow, there was a weird clicking noise coming from what sounded like behind the pump and with as many times as I have replaced parts, I no longer think that it's the pump head itself.

[Markus Laeubli, Metrohm]

Dear HGilliland21

Did you find an leak in the pump head after the pressure breakdown? If not, a total pressure drop is not originated by the piston or its seal.
Are the piston still moving after the dropdown? If yes, the problem most probably is one of the check valves.
Please check with your Metrohm representative for further support.

Best regards
Markus